Each year, tons of oil can be spilled into the ocean. Whether it comes from an oil tank spill, a leak that occurs during offshore drilling, or even natural seeps that occur within the ocean, oil spills can cause grave environmental and economic damage to marine and coastal ecosystems.

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When an oil spill occurs, the oil that floats on water will usually spreads out rapidly across the water surface to form a thin layer called an oil slick. As the oil continues spreading, the layer becomes thinner and thinner, eventually turning into a thin layer called a sheen. Managing and predicting the spread and path of oil is often very difficult for first-responders and clean up crews, however, a newly developed computer model holds promise to helping scientists track a spill.

U.S. Geological Survey scientists developed the model as a way of tracking the movement of sand and oil found along the Gulf of Mexico since the Deepwater Horizon oil spill.

Following the Deepwater Horizon spill, denser-than-water conglomerates of sand and oil have been found in the surf zone, ranging in size from less than a millimeter to mats up to a few meters in size. The surf zone is where waves break as they approach the shore. The USGS study looked at conglomerates several centimeters thick — known as "surface residual balls," or "SRBs", which continue to emerge in some beach locations more than three years after the first oil reached the shoreline.

Applying the model to movement of SRBs along the coast of Alabama and western Florida showed that normal wave conditions, less than 1.5 to 2 meters, will not move centimeter-sized SRBs alongshore. However, tropical storms, or winter storms can mobilize and redistribute these SRBs alongshore.

The numerical model indicated that inlets trap SRBs, where they could accumulate over time. The model also suggests that when larger SRBs are found they are more likely to have been formed locally when the oil came ashore, rather than being transported from a different location along the coast.

"The techniques developed here can be applied to evaluate the potential alongshore movement of SRBs in other locations or from any future spill where large quantities of oil and sand mix in the surf zone", said Dalyander.